Heat exchangers are commonly used to transfer heat from one region to another.
For example U.S. Pat. No. 227,334 discloses the use of an "L" shaped water back or heat exchanger which is equipped with a cold water pipe and a hot water pipe. The water back is placed adjacent an oven and water passing from the cold water pipe into the water back is heated from the transfer of heat energy from the oven to the water back, and exits the hot water pipe.
Moreover, various efforts have been made in order to maximize the extraction of heat energy from a heat source by utilizing heat exchangers as disclosed in U.S. Pat. Nos. 4,392,455, 4,403,573, 3,104,651, and 1,026,753.
U.S. Pat. No. 4,392,455 discloses a water heater system having a heat sink modual or heat exchanger that can be easily attached to an external wall of a wood-burning stove to transfer heat from the stove to water flowing through the modual to preheat water for subsequent household use.
In another arrangement disclosed in U.S. Pat. No. 4,403,573 a heat exchanger is fitted to the exterior wall of a wood-burning stove and connected in combination with a tank of water to be heated thereby.
U.S. Pat. No. 3,104,651 teaches the use of an auxilliary hot water heater which is supported within a fire chamber and surmounted by a water leg containing water to be heated by the fire chamber. The auxilliary heater absorbs heat energy faster than the inner surfaces of the water leg so as to more rapidly heat the water within the auxilliary water heater.
Furthermore, U.S. Pat. No. 1,026,762 discloses the use of a chamber which is formed integrally with the walls of the fuel and combustion chamber for heating water for household use.
Industrial ovens may also utilize a combustion chamber as a source of heat energy for cooking food products. More particularly a gas-fired steam generating oven usually comprises a boiler, combustion chamber and a heat energy source such as gas burner tubes. The boiler contains water which absorbs heat energy from the combusted gases in the combustion chamber and converts the water into steam.
Various efforts have been made to miximize the extraction of heat energy to vaporize the water into steam, including the use of coiled copper heat exchangers in the combustion chamber or within the boiler. Such combinations present complicated and expensive arrangements.
Moreover fresh water introduced into the boiler to replace the spent water converted into steam, drops the temperature of the water mixture and also the steam pressure, until the temperature of the water mixture once again reaches the boiling point. Inefficiency in cooking results from this drop in steam pressure.
Furthermore, this drop in steam pressure in the boiler causes the walls of the boiler to contact inwardly until the steam pressure once again builds up to its normal operating steam pressure; at which point the walls of the boiler expand outwardly. This cyclical inward and outward expansion of the boiler walls, or "flexing" of the boiler walls tends to fatique and weaken the boiler, particularly when the boiler walls are welded together.
Stayrods, which are metallic rods spanning the interior cavity of the boiler and welded to opposite walls thereof, have been used to absorb the flexing stresses of the walls, so as to strengthen and rigidify the boiler. However, over prolonged usage, even the stayrods fail, as for example, breakage of the weld between the stayrod and the walls of the boiler.